In human beings, Parkinson's disease (PD) is associated with the oligomerization and amyloid formation of α-synuclein (α-Syn). The polyphenolic Asian food ingredient curcumin has proven to be effective against a wide range of human diseases including cancers and neurological disorders. While curcumin has been shown to significantly reduce cell toxicity of α-Syn aggregates, its mechanism of action remains unexplored. Here, using a series of biophysical techniques, we demonstrate that curcumin reduces toxicity by binding to preformed oligomers and fibrils and altering their hydrophobic surface exposure. Further, our fluorescence and two-dimensional nuclear magnetic resonance (2D-NMR) data indicate that curcumin does not bind to monomeric α-Syn but binds specifically to oligomeric intermediates. The degree of curcumin binding correlates with the extent of α-Syn oligomerization, suggesting that the ordered structure of protein is required for effective curcumin binding. The acceleration of aggregation by curcumin may decrease the population of toxic oligomeric intermediates of α-Syn. Collectively; our results suggest that curcumin and related polyphenolic compounds can be pursued as candidate drug targets for treatment of PD and other neurological diseases.

α-Synuclein (α-Syn) aggregation is directly linked with Parkinson's disease (PD) pathogenesis. Here, we analyzed the aggregation of newly discovered α-Syn missense mutant H50Q in vitro and found that this mutation significantly accelerates the aggregation and amyloid formation of α-Syn. This mutation, however, did not alter the overall secondary structure as suggested by two-dimensional nuclear magnetic resonance and circular dichroism spectroscopy. The initial oligomerization study by cross-linking and chromatographic techniques suggested that this mutant oligomerizes to an extent similar to that of the wild-type α-Syn protein. Understanding the aggregation mechanism of this H50Q mutant may help to establish the aggregation and phenotypic relationship of this novel mutant in PD.

Mechanistic understanding of nucleation dependent polymerization by α-synuclein (α-Syn) into toxic oligomers and amyloids is important for the drug development against Parkinson's disease. However the structural and morphological characterization during nucleation and subsequent fibrillation process of α-Syn is not clearly understood. Using a variety of complementary biophysical techniques monitoring entire pathway of nine different synucleins, we found that transition of unstructured conformation into β-sheet rich fibril formation involves helix-rich intermediates. These intermediates are common for all aggregating synucleins, contain high solvent-exposed hydrophobic surfaces, are cytotoxic to SHSY-5Y cells and accelerate α-Syn aggregation efficiently. A multidimensional NMR study characterizing the intermediate accompanied with site-specific fluorescence study suggests that the N-terminal and central portions mainly participate in the helix-rich intermediate formation while the C-terminus remained in an extended conformation. However, significant conformational transitions occur at the middle and at the C-terminus during helix to β-sheet transition as evident from Trp fluorescence study. Since partial helix-rich intermediates were also observed for other amyloidogenic proteins such as Aβ and IAPP, we hypothesize that this class of intermediates may be one of the important intermediates for amyloid formation pathway by many natively unstructured protein/peptides and represent a potential target for drug development against amyloid diseases.

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α-Synuclein (α-Syn) oligomerization and amyloid formation are associated with Parkinson's disease (PD) pathogenesis. Studying familial α-Syn mutants associated with early onset PD has therapeutic importance. Here we report the aggregation kinetics and other biophysical properties of a newly discovered PD associated Finnish mutation (A53E). Our in vitro study demonstrated that A53E attenuated α-Syn aggregation and amyloid formation without altering the major secondary structure and initial oligomerization tendency. Further, A53E showed reduced membrane binding affinity compared to A53T and WT. The present study would help to delineate the role of A53E mutation in early onset PD pathogenesis.